1. Field of the Invention
This invention relates to a network communication system for use in handling communications between access units which may comprise office automation systems, telex, teletex, facsimile, etc.
Abbreviations and acronyms used herein are listed at the end of the description. References to Data General are to Data General Corporation, the assignees of the present application.
2. Description of the Prior Art
There exist today many proprietary communications systems and various international standards relating to message handling and data transmission. Nevertheless there is no system in existence which will allow all kinds of access units to communicate freely with one another.
It is true that there do exist gateway systems, known commercially as Soft-Switch and Mailbus which are intended to allow interchange of messages between dissimilar systems. However these known systems are essentially suitable for use by private corporate and other large users because they utilize a proprietary message transfer protocol handled via a central processing system which converts from and to the message protocols employed by the various gateways. Moreover they are set up as complete systems in which each gateway has to know what other gateways there are on the system and what are the characteristics of the various gateways.
The known systems are neither intended for nor suitable for public services.
Another problem with which the invention is concerned arises in conjunction with computer operating systems (e.g. MS-DOS and UNIX) which are single threaded, i.e. they can handle only a single processing thread at a time. This leads to the result that routines frequently have to wait if the processing path comes to a halt while waiting for an external event. The routine is said to pend. Although other operating systems can handle multiple threads (e.g. AOS/VS) the system according to the invention is desirably not restricted to a particular operating system and should be capable of operating with single threaded operating systems. Some systems, e.g. UNIX can simulate multitasking by holding a plurality of copies of a program in memory and scheduling the allocation of the CPU to the different processes. However this is wasteful of memory resources. MS-DOS has no built-in facilities for achieving even this level of multi-tasking.
In a network communication system waiting for events occurs all the time, e.g. as transfers are effected across interfaces, and single threaded systems lead to inefficient usage of computer resources, for the reasons explained above.